<p>We draw carbon dioxide into our bodies and release it with every breath. Plants need it to survive. How did a gas essential to life become a demonized pollutant that could alter the world's environment as we know it?</p>
<p>Carbon dioxide is one of the Earth's so-called greenhouse gases, which in increasing amounts can heat up the atmosphere. Increased heat may lead to wholesale changes in climate, disrupting the way plants, wildlife and people live all over the planet.</p>